This invention relates to xerographic reproducing apparatus and, in particular, to apparatus for removing toner particles from a charge retentive surface.
More specifically, this invention relates to improved apparatus for cleaning charged toner particles from an electrostatic recording surface of the type suitable for use in the automatic xerographic reproducing process. In the xerographic process, a uniform electrostatic charge is placed upon a photoconductor or photoconductive surface and the charged surface then is exposed to a light image of an original so as to selectively dissipate the charge to form a "latent electrostatic image" of the original. The latent image is then developed by depositing finely divided charged toner particles upon the photoconductive surface, the charged toner being electrostatically attracted to the "latent electrostatic image" areas to create a visible replica of the original. The developed image is then usually transferred from the photoconductive surface to a final support material and the toner image is fixed thereto to form a permanent record corresponding to the original.
In the practice of automatic xerography, a photoconductive surface is generally arranged to move in an endless path through the various processing stations of the xerographic process. When the photoconductive surface is reusable the toner image is then transferred to a final support material such as paper or the like, and the photoconductor is prepared to be used once again in the reproducing process. Although a preponderance of the toner image is transferred to the final support material during the transfer operation, some of the toner material forming the image commonly referred to as residual toner is unavoidably left behind on the photoconductive surface. This residual toner must be removed from the surface in some manner to avoid degrading subsequent copies reproduced on the photoconductor. Optimumly, the residual toner is removed without redeposition onto the photoconductor.
One of the most successful and widely used methods of cleaning residual toner material from a photoconductive surface is by means of a brush rotated in contact with the photoconductor at a relatively high rate of speed. U.S. Pat. No. 2,832,977 issued to Walkup discloses a rotatable brush mounted in close proximity to the photoconductive surface to be cleaned and the brush is rotated so that the brush fibers continually wipe across the photoconductor in a manner to produce the desired cleaning. In order to reduce the dirt level within the machine, a vacuum system is provided which pulls loosely held residual toner particles from the brush fibers and exhausts the toner from the apparatus. To assist the vacuum system in removal of the toner material, Walkup treats his brush fibers with a neutralizing ion spray which is intended to negate any triboelectrification generated when the brush wipes across the photoconductive surface. Although the Walkup vacuum and neutralization system is capable of reducing the dirt level by removing loosely held soils from the brush fibers, it has been found that the brush nevertheless becomes contaminated after extended usage to a point where the brush must be replaced within the cleaning system.
With the advent of new processing techniques and toner materials, machine speeds have now reached a level where the foregoing brush cleaning technique can no longer be effectively utilized. In order to overcome some of the difficulties found in the art, while at the same time preserving the advantages of brush cleaning, Fisher et al in U.S. Pat. No. 3,572,923 devised a cleaning apparatus adapted for use in a high speed automatic reproducing machine. In Fisher, a fibrous cleaning brush, similar to that disclosed by Walkup, is used to remove residual toner particles from a photoconductive surface. However, after the photoconductive surface is cleaned, a second cleaning operation is performed on the brush in which residual toner material collected on the brush is electrostatically transferred from the brush fibers to a biased transfer member. In order to create the proper electrostatic relationship between the cleaning members, Fisher supports his fibrous brush upon a non-conductive core and biases the core in a manner to attract toner from the photoconductive surface toward the brush. Although the biased core arrangement has proven to perform satisfactorily, it has been found that a more efficient cleaning operation can be effected when an electrostatic relationship is established between the brush fiber and the transfer member.
Accordingly, as disclosed in U.S. Pat. No. 3,722,018 a corona generator is positioned to induce a charge in the brush fibers and particles thereon of a polarity opposite that of a biased transfer roll whereby the particles collected by the brush are efficiently transferred from the brush to the roll.
Toner removal from the brush can also be accomplished by the use of an electrically biased flicker bar as illustrated in U.S. Pat. No. 3,780,391 granted to Leenhouts. The Leenhouts device also uses an electrically biased bar which charges the brush prior to its contact with the photoconductor.
Numerous other prior art cleaning devices differing somewhat from those discussed hereinabove have been developed for removing toner from a photoconductor. Most if not all of them utilize some sort of electrical biasing scheme to establish suitable electrostatic forces for either attracting or repelling the charged toner particles.
Methods of creating suitable electrostatic forces without the undesirable expense of electrical biasing arrangements such as discussed above employ one or more flicker bars supported within the cleaner housing such that there is an interference with brush movement which causes the brush fibers to be flexed with subsequent return thereof to their unflexed position. Such flexing causes a flicking action. With such a cleaning device it has been observed that toner redeposits on the photoconductor particularly under stress conditions. Stress conditions are the use of an older brush, extreme envirnonmental conditions such as high relative humidity, solid area residual toner, trying to clean some of the finer toner particles which have recently come into use and high preclean biases.
Certain xerographic machines experience what has come to be referred to as the extended line problem. Simply stated, it is the inability of the brush cleaner to remove lines that come to the cleaner straight-on. One way of solving the extended line problem is to increase the preclean bias. However, when increasing the preclean bias it was discovered that the increased charge on the photoconductor aggravated the redeposition problem.
Thus, what is needed is a brush cleaning apparatus which is relatively inexpensive and which is capable of extending the life of the brush, better able to remove solid area residual toner, possesses a greater operational latitude and precludes redepositon.